Problem with testing WB (heater circuit)

[bcroe at juno.com]

Sounds good!  Yes the sensor may be still finishing
warm up when the LED comes on.  Should be OK
(we hope!).  

Your meter should be connected directly to the WB
terminals; a connection to the car body will add more
error.  If the 2.5V reference is off, the same error will 
appear in readings.  I would consider 3.96V plenty 
good enough for normal work; 0.1% resistors are 
expensive.

Bruce Roe

On Wed, 30 Jan 2002 10:04:29 -0500 Brian Renegar
<thomas.renegar at nist.gov> writes:
> 
> >Looks like C3 is OK; it would probably get hot if bad.  Check
> >putting 14 volts on the supply; 13.5V is marginal.
> >
> >Bruce
> 
> Well, I figured it out.  Dumb old me had the LED in 
> backwards.  D'oh!  Works better the correct way.  :)  Currently 
> I have one resistor (15 Ohm I think is what Steve added 
> to the kits) added to R4.  LED comes on in 45-50 seconds.  
> Current draw through the heater is 1.402A, which reduces 
> to approx. 1.28A once the sensor is hot.  Vout is between 
> 3.96 and 3.97 V.  Is that close enough??  I know it's 
> supposed to be 4.00V, but due to variation in components, 
> am I ok?  One other question though...  After the LED turns 
> on, it appears to still take 10-15 seconds for the Vout to 
> stabilize.  It ramps up and then tapers off at 3.97V.  Is that 
> normal?  Is the sensor still heating up, or is something else 
> going on?
> 
> Thanks for the help,
> Brian

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